Cardiovascular disorders and diseases, and their associated complications are a principal cause of disabilities and deaths of individuals in the United States and Western Europe. For example, in recent years more than 500,000 deaths have occurred annually in the United States alone as a result of coronary artery disease, and an additional 700,000 patients have been hospitalized for myocardial infarction.
There has been an ongoing search for effective long term treatment for disorders and diseases of the heart and arteries, such as atherosclerosis, arteriosclerosis, congestive heart failure, angina pectoris, and other disorders and diseases associated with the cardiovascular system. Prior treatments for such disorders or diseases include administration of vasodilators, angioplasty and by-pass surgery, for example. Such treatments have met with disapproval due to the risks versus the benefits gained by the various treatments. Moreover, such treatments have serious shortcomings in long term effectiveness. The use of vasodilators drugs and mechanical treatments for acute and chronic occlusive vascular diseases of the heart, central, and peripheral vascular system have to date been ineffective for favorable long term results. The outcome with current treatments is minimally impacted because the treatments are directed toward the effects of the underlying disease process rather than the initial molecular cause of the disease or disorder.
For example, the rationale for vasoactive drugs is to reduce blood pressure by acting directly or indirectly on vascular, and/or cardiac, smooth muscle and thereby decreasing vascular resistance and abnormalities to flow. Such drugs do not treat the initial cause of elevated pressure and abnormal flow. Rather, they seek to reduce the resulting effect of the disease or disorder. Such drugs activate the sympathetic nervous system by way of the baroreceptor reflex to produce an increased heart rate and force of myocardial contraction which are not necessarily always beneficial effects. Other side effects from such drugs include headache, heart palpitations, anxiety, mild depression, dry-mouth, unpleasant taste in the mouth, nausea, vomiting, angina, myocardial infarction, congestive heart failure, decreased cardiac output, fluid retention, fatigue, weakness and others. Pharmacological treatment of most diseases is not very specific in its effect on the initial molecular cause of the disease activity, and treats a very limited spectrum of effects in diseases which are multi-factorial.
As a further example, such improved outcome in atherosclerotic vascular diseases is seen with cholesterol reduction and drug treatment for lipid disorders. However, these treatments do not treat the clotting abnormalities associated with these disease states which are known to be the proximate event causing heart attack and stroke. These do not prevent the cellular or molecular reactions attributed to platelets, macrophages, neutrophils, lymphocytes, smooth muscle cells, and other cell types known to be involved in atherosclerosis and complications of the disease.
Likewise, thrombolytic therapy, angioplasty and by-pass surgery have been minimally successful long term. Current mechanical and pharmacological treatments focus on a particular partial or complete occlusion or occluded vessel where, at the particular site, it is either unclogged or by-passed with connecting vessels. These treatments fail to address the physiologic derangements of normally homeostatic systems which allow the occlusive process to begin and progress. Likewise, they fail to address the multi-centric nature of the homeostatic derangements. These failures frequently result in recurrent occlusion in the initially treated vessel, and in microemboli from incomplete resolution of thrombus at the occlusive site treated. No treatment is available for sites judged to be inadequately occluded or stenotic that would respond to currently available, crude technologic methods.
There remains a great need for treatment which prevents the failure of the normal homeostatic controls and which restores these controls once derangements begin to develop. Restoration of the endogenous regulatory systems and cellular domains to a healthy state could prevent the stenosis, occlusion, thrombosis, and thromboembolic processes which occur as a consequence of such derangements. Continuous and episodic restoration of control in the normal molecular processes which finely regulate homeostasis can prevent atherosclerosis, variants thereof, hypertension, congestive heart failure, macro and micro-thrombosis and thromboembolism, and complications of these disease processes, including, but not limited to, myocardial infarction, cerebrovascular accident, related kidney diseases, related central and peripheral nervous system disorders, and related diseases in other cellular systems. In addition, rapid restoration of homeostatic control once injurious processes accelerate and accumulate can minimize both the extent of and duration of consequences on atomic, molecular, membrane, cellular, and organ levels.
Epoprostenol (PGI2, PGX, prostacyclin), a metabolite of arachidonic acid, is a naturally occurring prostaglandin with potent vasodilatory activity and inhibitory activity of platelet aggregation. Epoprostenol is (5Z,9(alpha),11(alpha),13 E,15 S)-6,9-epoxy-11,15-dihydroxyprosta-5,13-dien-1-oic acid. Epoprostenol sodium has a molecular weight of 374.45 and a molecular formula of C20H31NaO5, and was approved by the U.S. FDA as Flolan (marketed by GlaxoSmithKline) on Sep. 20, 1995, to treat patients with cardio obstructive pulmonary disease.
Flolan for Injection is a sterile sodium salt of epoprostenol formulated for intravenous (IV) administration. Each lyophilized vial of Flolan contains epoprostenol sodium equivalent to 0.5 mg or 1.5 mg epoprostenol, 3.76 mg glycine, 2.93 mg sodium chloride, and 50 mg mannitol. Sodium hydroxide may also be added to adjust pH.
Flolan is a white to off-white powder that must be reconstituted with sterile diluent for Flolan. Sterile diluent for Flolan is supplied in glass vials containing 94 mg glycine, 73.5 mg sodium chloride, sodium hydroxide (added to adjust pH) QS to 50 ml Water for Injection, USP. The reconstituted solution of Flolan has a pH of 10.2 to 10.8 and is increasingly unstable at lower pH.
Epoprostenol sodium (Formula I), an exocyclic vinyl ether, hydrolyzes rapidly, in a pH dependent fashion, to 6-keto-PGF (Formula II). Formula I and Formula II are as follows:

The chemical nature, especially the potential hydrolytic lability, of epoprostenol makes it very difficult to develop a robust formulation. The vinyl ether moiety of PGI2-Na is best stabilized in solution by buffering under basic conditions (>pH 8.8). The half-life, time required for 50% lost in potency, of epoprostenol sodium in water as function of pH is tabulated below in Table 1:
TABLE 1Solution stability of Epoprostenol in pH 7.2 to 9.3Temperature (C.)pHHalf-life (hours)08.921.0238.94.4239.310.33237.20.033As shown in the above Table 1, 50% of epoprostenol degrades in about 10 hours at pH 9.3 at 23° C. In order to manufacture a sterile dosage form, the compound should not lose potency for at least 12 hours preferably under ambient conditions. If this is not achievable, the compound must be stable at 4° C. for about 12 hours to process under chilled conditions.
Flolan is supplied as a lyophilized vial with a companion vial which consists 50 ml of a special diluent buffered with glycine and made isotonic with sodium chloride. The pH of the isotonic solution is adjusted to a range of 10.2 to 10.8 with sodium hydroxide. The lyophilized vial is reconstituted with the special diluent and administered to patients suffering from cardiovascular disorders.
Flolan must be reconstituted only with this sterile diluent for Flolan. Reconstituted solutions of Flolan must not be diluted or administered with other parenteral solutions or medications. The reconstituted solutions of Flolan must be protected from light and must be refrigerated at 2° to 8° C. (36° to 46° F.) if not used immediately. The refrigerated solution, however, only lasts two days and must be discarded thereafter. Additionally, the reconstituted solution cannot be frozen, and the solution must be discarded if it is frozen.
Therefore, there remains a need for epoprostenol formulations that can be reconstituted with commercially available IV fluids and do not require refrigeration after reconstitution until use.